This invention relates to a photosensitive composition. Particularly, it relates to a photoresist (a photosensitive, etching-resistant coating material) having high resolution which is suitable for fabricating semiconductor devices.
For improving the performance characteristics of semiconductor devices such as IC, LSI and the like, it is necessary to improve the fineness of their fabrication. Therefore, a photoresist used for the fabrication is required to have particularly high resolution.
As is generally known, photoresists are divided into two groups, i.e., positive type and negative type. Almost all of positive type photoresists used for fabricating semiconductor devices are obtained by mixing an alkali-soluble phenolic resin as a film-forming component with a naphthoquinone diazide derivative as a photosensitive component. Almost all of negative type photoresists used for fabricating semiconductor devices are obtained by mixing a cyclized rubber with an aromatic bisazide as a photosensitive component.
When there is made a comparison between the resolutions of the above-mentioned two kinds of photoresists, the resolution of the positive type photoresists is superior to that of the negative type photoresists. Therefore, the positive type photoresists have come to be often used for recent fabrication of high-performance semiconductor devices.
The reason why the resolution of the positive type photoresists is higher than that of the negative type photoresists is as follows. The contrast of the positive type photoresists is higher than that of the negative type photoresists and the positive type photoresists are developed without their swelling with a developer. On the other hand, the negative type photoresists are swollen with a developer, so that their patterns are lost or deformed in some cases.
Accordingly, the negative type photoresists also can be expected to have high resolution if their contrast is high and they are not swollen with a developer.
Among photoresists used for uses other than fabrication of semiconductor devices, there are known negative type photoresists which are not swollen with a developer. For example, it is well known that a mixture of an alkali-soluble phenolic resin and an aromatic azide can be utilized as a negative type photoresist for fabrication of photographic printing plates, and this photoresist does not undergo swelling phenomenon when developed with an aqueous alkali solution. Japanese Patent Publication No. 22082/70 discloses a negative type photoresist containing an aromatic azide compound and an alkali-soluble phenol-formaldehyde resin, and Japanese Patent Publication No. 34902/78 discloses a negative type photoresist containing an aromatic azide compound and a polymer of hydroxystyrene.
However, few cases are known where these photoresists are utilized for fabricating semiconductor devices. The reason for this is that these photoresists have been developed mainly for the purpose of utilizing them for fabrication of photographic printing plates, and are suitable for utilization in the form of a coating film having a thickness of several tens microns but have not always been suitable for utilization in the form of a coating film which has a thickness of several microns to about 0.1 micron like a coating film used in fabrication process of semiconductor devices.
Further, for improving the performance characteristics of a semiconductor device, micro-fabrication is necessary, therefore in fabricating a semiconductor device, a fine pattern of photoresist is often formed by using a reduction projection printer. Usually, the optics of a reduction projection printer do not transmit UV light but transmit the light with wavelengths longer than 400 nm. The wavelengths of light of a high pressure Hg lamp as a light source include 405 nm, 436 nm, etc. in the visible region, and light having a high intensity is one which has a wavelength of 436 nm, i.e., light called "g-line". Accordingly, only photoresists which are hardened by this light having the wavelength of 436 nm permit employment of a reduction projection printer. The above-mentioned conventional negative photoresists are hardly photosensitive to the light having the wavelength of 436 nm and are not hardened thereby.